Electroluminescent lamp construction



Aug. 25, 1959 E. G. FRIDRICH ELECTROLUMINESCENT LAMP CONSTRUCTION FiledDec. 10, 1957 lnvervtof: Ebmev GfridT-ich,

United States Patent ELECTROLUMINESCENT LAMP CONSTRUCTION Elmer G.Fridrich, Cleveland, Ohio, assignor to General Electric Company, acorporation of New York Application December 10, 1957, Serial No.701,894-

4 Claims. (Cl. 313-108) This invention relates to electroluminescentlamps of the flexible laminated type and is more particularly concernedwith the contacts or terminals of such lamps for the application ofvoltage thereto.

An electroluminescent lamp or cell comprises a layer of phosphorsandwiched between a pair of conducting plates or films at least one ofwhich is transparent or light-transmitting. The electroluminescent cellof the present invention is of the type disclosed in Patent2,774,004Jatfe, assigned to the same assignee as the present invention,wherein the transparent conducting plate or layer is a flexibleconductive sheet of compacted glass fibers. More specifically, thepresent invention is proposed as an improvement over theelectroluminescent lamp construction described and claimed in copendingapplication Serial No. 701,906 of Elmer G. Fridrich and Paul A. Dell,filed of even date herewith, and entitled Electroluminescent Lamp andManufacture Thereof, and assigned to the same assignee as the presentinven- *tion. The electroluminescent lamp described therein comprises aflexible laminated assembly of electrically active layers encased in athin envelope of thermoplastic material which is evacuated andcompletely heat-sealed all around its edges. The electrically activeelements comprise an aluminum foil coated with a layer of highdielectric constant material which in turn is overcoated with a layer ofelectroluminescent phosphor. Overlying the phosphor layer is a sheet ofconducting glass paper which extends less than all the way to the edgesof the aluminum foil. The contacts or terminals of the lamp compriseflattened metal conductors or ribbons extending one in contact with theouter surface of the aluminum foil, and the other in contact with theouter surface of the conducting glass sheet, these metal ribbons beingembedded one in each of the outer sheets of the thermoplastic envelope.The ends of the ribbons are connected to pieces of fine copper meshWhose inner ends are embedded in the thermoplastic envelope and whoseouter ends project therefrom to provide the terminals of theelectroluminescent lamp.

The object of the present invention is to provide a new and improvedterminal construction for such an electroluminescent lamp.

A more specific object of the invention is to provide a terminalconstruction which is complementary to the thin flat nature of theflexible electroluminescent lamp and which will lend itself readily toengagement in a correspondingly fiat socket into which the lamp mayeasily be inserted. Another object is to provide a terminal constructionallowing an electroluminescent cell to be cut into sections with eachsection retaining suitable terminals.

Yet another object of the invention is to provide a ter minalconstruction for such electroluminescent lamp-s which is adaptable tocontinuous strip production.

In accordance with the invention, a laminated flexibleelectroluminescent lamp or cell is provided with electrode strips alongat least one edge consisting of a pair of foils separated by aninsulating sheet of plastic, one of the foil electrodes being incontinuous contact with the aluminum foil of the cell and the otherbeing in continuous contact with the conducting glass sheet.

In a preferred construction, the phosphor coated foil of the cell has aportion devoid of phosphor extending beyond the edge of the polyethyleneenvelope on one side and is folded thereover to lie fiat against theunderside of the cell along one margin. A high-density polyethylenestrip is inserted along the margin of the cell to cover the bare marginof the foil up to where it is bent around the polyethylene envelope. Forthe other electrode, a foil strip is placed to overlie the edge of theconducting glass paper and is bent around to overlie the upperside ofthe polyethylene envelope. The cell is thus provided with exposedcontinuous strip contacts on opposite sides of one margin of theenvelope which may readily be engaged by a clamp type connector forenergizing the cell.

For further objects and advantages and for a detailed description ofpreferred embodiments of the invention, attention is now directed to thefollowing description and accompanying drawings. The features of theinvention believed to be novel will be more particularly pointed out inthe appended claims.

In the drawings:

Fig. l is a pictorial view of a flexible laminated electroluminescentlamp embodying the invention, along with a suitable connector therefor.

Fig. 2 is a detailed exploded sectional view of the elfetl trodeterminal edge of the electroluminescent lamp 0 *ig. 1.

Fig. 3 is a view similar to that of Fig. 2 showing a variant of theinvention.

Referring to Fig. l, the illustrated electroluminescent lamp has onecorner delaminated or peeled open to show the various constituent layersof the lamp. The cell 1 is a flat rectangular device made up entirely offlexible components laminated together and entirely sealed in plasticmaterial. The lowermost film or sheet 2. and the uppermost sheet 3 whichform respectively the underside and the topside of the envelope in thefinished lamp consist of thermoplastic material which flows under heatand pressure and welds or fuses together along the margins. Thethermoplastic material selected, in addition to being light-transmittingand preferably fairly flexible, must be reasonably tough and stable andhigh-density polyethylene film of 0.003 inch thickness is preferred. Arectangular sheet of thin metal foil 4 coated with an insulating layer 5of high dielectric constant material and a light producing layer 6 ofelectroluminescent phosphor is placed over the lowermost polyethylenesheet 2 leaving a clear margin all around. A sheet of conductingmicrofiber glass paper 7 is laid over the coated foil leaving a narrowmargin of foil uncovered all around. Preferably a thinner sheet or film8 of low-density polyethylene is placed over the conducting glass paperand conveniently is of the same size as the high-density polyethyleneenvelope sheets 2, 3 and extends to their margins.

The coated metalvfoil 4 may consist of dead-soft annealed aluminum of0.0008" thickness coated witha thin insulating layer such as bariumtitanate dispersed in an organic polymeric matrix and over-coated withan electroluminescent phosphor such as zinc sulfide with a suitableactivator and likewise dispersed in an organic polymeric matrix. Apreferred organic polymeric matrix forming a dense tough film of highdielectric constant and good mechanical and thermal stability andconsisting of cyanoethyl cellulose with a suitable plasticizer is de-'scribed and claimed in copending application Serial No. 701,907 of MaryS. Jatfe, entitled High Dielectric Constant Matrices forElectroluminescent Phosphors, filed with stannic chloride (SnCldissolved in an organic solvent such as ethylene glycol monoethyl etheracetate. Reference may be made to copending application Serial No.347,617 filed April 8, 1953 of Mary S. Jatfe entitled Conductive Coatingon Glass, now US. Patent 2,849,- 339 for a more complete description ofthe materials and process used in making conducting glass paper.

In order to energize the electroluminescent lamp, it is necessary toapply an alternating potential across the conductive layers, that is tothe aluminum foil 4 and to the conducting glass paper 7. Convenientelectrodes or contacts for so doing are provided consisting of metalfoil strips 10, 11 extending along one margin and overlying the plasticenvelope, the strips being separated and insulated one from the other bymeans of a plastic insert strip 12 extending slightly beyond what wouldotherwise be the edge of the lamp along that margin.

The details of construction of the contact strips are best shown in Fig.2 which is in the nature of an exploded sectional view. In the completedlamp, of course, the components shown in Fig. 2 are pressed andlaminated together and appear as shown in Fig. 1. Referring to Fig. 2,aluminum foil 4, generally coated with a bariurn titanate layer 5 andovercoated with a phosphor layer 6, is provided with a margin 13 devoidof coating. This margin extends to and around the edge of the lowerhighdensity polyethylene envelope sheet 2 and forms lower contact strip10. Preferably, a heat-sensitive laminating adhesive is applied to themargin of the high-density polyethylene sheet 2 to assure betteradhesion between the polyethylene and the aluminum foil where they join.The adhesive, for instance a silicone cement, may be applied by brushingon the edge of the high-density polyethylene sheet 2.

A narrow strip of high-density polyethylene is placed over the baremargin of foil 4 and forms the insulating polyethylene strip 12previously mentioned with reference to Fig. 1. Strip 12 extends farenough inwardly into the cell lay-up to underlie the conducting glasspaper 7 and extends far enough outwardly to provide protectiveinsulation between lower contact 10 and upper contact 11. A thin strip14 of soft low-density polyethylene (shown at an angle in Figs. 2 and 3for illustrative purposes) is interposed between the edge of theinsulating polyethylene strip 12 and the conducting glass paper 7. Strip14 eases the abruptness of the step which the conducting glass papermust make in going over the edge of insulating strip 12 of high-densitypolyethylene when the lamp is laminated; the glass paper after it hasbeen made conducting is quite fragile and rather brittle and mightotherwise break at the step. Strip 14 also improves the adhesion of thecell components at the margin.

The upper contact consists of an aluminum foil strip 15 overreachingconducting glass paper 7 and extending out around the edges oflow-density polyethylene film 8 and high-density polyethylene envelopesheet Sand folded around the latter to form upper contact strip 11. Themargin of high-density polyethylene upper envelope sheet 3 is likewisepreferably coated with a heat-sensitive laminating adhesive to insuregood bonding of contact strip 11 to the lamp envelope.

Connections to the contact surfaces may conveniently be made by means ofthe flat connector shown at 16 in Fig. 1 and consisting of a moldedpiece of insulating plastic material 17, channel-shaped in cross sectionto provide a groove 18 which may be slipped over the edge of theelectroluminescent lamp to overlap the contacts. Within the groove 18are positioned a pair of spaced connectors 19, 20 each provided withspringy tongues 21, 22 forming two staggered series electricallyinsulated one from the other. The tongues of series 21 engage lowercontact strip 10 and those of series 22 engage upper contact strip 11.The twisted wires 23, 24 are connected respectively to series 21, 22 andlead to a voltage source; the staggering of the tongues avoidsshortcircuiting the wires when the connector is disengaged from thelamp.

Referring to Fig. 3, there is shown a variant of the invention whereinthe contact strips, instead of being folded over the edge of theelectroluminescent lamp envelope, are merely extended out flat to theside. This makes for easier assembly on a continuous-strip productionbasis. As illustrated, coated aluminum foil 4 is extended beyond theedge of high-density polyethylene envelope sheet 2 as a non-coated strip26. High-density polyethylene insulating strip 12 is made wider than inthe embodiment of Fig. 1 in order to reach and project slightly beyondthe outer edge of the laterally projecting contact strips. The uppercontact strip 27 overreaches the conducting glass paper 7 on one sideand extends even with the edge of contact strip 26 on the other side.The high-density polyethylene insulating strip 12 is preferably coatedwith a heat-sensitive laminating adhesive on both sides to insure goodbonding of the aluminum foil contact strips.

In the embodiment of Fig. 3, it is not essential that the margin ofaluminum foil 4 be devoid of the barium titanate and phosphor layersinasmuch as it is the underside of the foil which is engaged by theconnector.

However it is preferable to have at least the outer edge devoid ofphosphor in order to assure a good bond between aluminum foil 4 andhigh-density polyethylene insulating strip 12, and also to provide amore effective hermetic seal with greater resistance to penetration ofmoisture.

It will be appreciated that instead of having both contact strips onopposite sides of the same margin of the electroluminescent lamp, thestrips may be provided on opposite mar ins or spaced longitudinal alongthe same margin in which case, of course, both contact strips may beplaced on the same side of the electroluminescent lamp if desired, forinstance on opposite edges of the front face. Obviously, a number ofvariations of this kind are possible with the strip construction whichhas been described. The contact strip construction of the inventionlends itself particularly well to continuous band production techniquesinasmuch as any particular length cut 01f from the band has a portion ofthe contact strip attached ready to serve as terminals.

While certain specific embodiments of the invention have been describedin detail, the same are intended as illustrative and not in order tolimit the invention thereto. The scope of the invention is to bedetermined by the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electroluminescent cell comprising a laminated evacuated assemblyincluding outer envelope sheets of thermoplastic material of which atleast the front sheet has a light-transmitting portion and anelectrically active assembly including a thin flexible metal foil havinga coating of electroluminescent phosphor and a sheet of conducting glassfibers facing said coating, said outer envelope sheets being sealedtogether along their margins and overreaching the electrically activeassembly, and a pair of contact foils extending out of said laminatedassembly and separated by and laminated to an intermediate thermoplasticstrip serving as an insulator, one of said contact foils being aprolongation of the metal foil of the electrically active assembly andthe other of said contact foils being a strip laid under the frontthermoplastic envelope sheet and over-reaching the margin of theconducting glass sheet and in conductive engagement therewith.

2. An electroluminescent cell comprising a laminated evacuated assemblyincluding an outer envelope of polyethylene sheets sealed together alongtheir margins and an electrically active assembly including an aluminumfoil having a coating of electroluminescent phosphor and a sheet ofconducting glass fibers facing said coating, said outer envelope sheetsoverreaching the electrically active assembly, and a pair of contactfoils extending out of said laminated assembly and separated andlaminated to an intermediate polyethylene strip serving as an insulator,one of said contact foils being a prolongation of the aluminum foil ofthe electrically active assembly and the other of said contact foilsbeing a strip laid under the overlying polyethylene envelope sheet andoverreaching the margin of the conducting glass sheet and in conductiveengagement therewith.

3. An electroluminescent cell comprising a laminated evacuated assemblyincluding outer envelope sheets of thermoplastic material and anelectrically active assembly including a thin flexible metal foil havinga coating of electroluminescent phosphor and a sheet of conducting glassfibers facing said coating, said outer envelope sheets being sealedtogether along their margins and overreaching the electrically activeassembly, and a pair of contact foils extending out one edge of saidouter envelope and folded back and laminated against opposite sides ofsaid envelope along a margin thereof, one of said contact foils being aprolongation devoid of phosphor of the metal foil of said electricallyactive assembly and the other of said contact foils being a strip laidunder the front thermoplastic envelope sheet and overreaching the marignof said conducting glass paper, and an intermediate thermoplastic striplaminated between said contact strips.

4. An electroluminescent cell comprising a laminated evacuated assemblyincluding outer envelope sheets of thermoplastic material and anelectrically active assembly including a thin flexible metal foil havinga coating of electroluminescent phosphor and a sheet of conducting glassfibers facing said coating, said outer envelope sheets being sealedtogether along their margins and overreaching the electrically activeassembly, and a pair of contact foils having marginal portions extendingout one edge of said outer envelope and laminated to opposite sides ofan intermediate insulating thermoplastic strip projecting out said edgeof said envelope, one of said contact foils being a prolongation of themetal foil of said electrically active assembly and the other of saidcontact foils being a strip laid under the front thermoplastic envelopesheet and overreaching the margin of said conducting glass sheet and inconductive engagement therewith.

References Cited in the file of this patent UNITED STATES PATENTS1,345,754 Dubilier July 6, 1920 1,889,522 Bailey Nov. 29, 1932 2,262,791Bransford et al. Nov. 18, 1941 2,774,004 Jafie Dec. 11, 1956 FOREIGNPATENTS 746,669 Great Britain Mar. 21, 1956

